I am building an app that uses a async socket connection with a web server.
For sending large amounts of data I would like to connect two iPhones into a Peer to Peer connection using an async socket. I am more familiar with GCDAsyncSocket than to the iOS SDK socket API.
I have done something similar, but only within a local network were I would user NSNetService to publish a presence and get the addresses needed from the p2p connection.
Can you give me a hint on how to connect two iPhone over the internet using a p2p socket connection?
I do not know much about NSNetService but it seems that it only works in a local network. If you want to establish a p2p connection from an iphone to another you will always have the problem of several NATs (Network address translators) in your route. How to find the address and route to the peer? And how to get trough all the firewalls and NATs?
I am working on an app that needs to deal with the same problem and I have answered a similar question before which I will cite here:
Actually, it IS possible. You may want to google for something called
"UDP hole punching" or "TCP hole punching".
The main approach in short: Assuming you got something like a relay
server, that is some server in the internet that is publicly
addressable from every private LAN that is connected to the www. No
you have your two clients A and B in (different) private LANs, with
some Network address translation (NAT) going on, that want to
establish a peer to peer connection.
First of all both will tell the server their IP address and the port
they have in their own LAN. In the UDP or TCP packet, the server will
find the public address and port of the device (or the NAT (router)).
So the server knows the private and the public IP address as well as
the ports.
If now A wants to communicate with B, it asks the server for help. The
server will send a message to B that A wants to communicate with her
telling her A's public and private IP and port. A gets back B's public
and private information and port.
Now here is where the magic happens. Both clients now send packets out
to establish a connection simultaneously to the private and public
addresses of the other party and thus punching a whole in their NATs
such that incoming connections will not be blocked. Even if one
party's connection establishing packets will arrive before this whole
is created, the other's packets will get through to such that a
connection can be created.
Beware of some NATs that scan the data for IP addresses and translate
them as well, but if you encrypt your data or change the appearance of
the address (complement, ...) you will be fine.
Now the master question, how can the server communicate with one of
the clients without an active connection. Well in this case you can
use "connection reversal" and apple's "push notifications". Use the
"push notifications" (pn) to tell a client behind a NAT that there is
something of interest going on and that it should contact the server.
Once it has done that the connection is active and can be used in the
previous described fashion.
I hope this helps some people that get to this problem although the
post is quite old!
Now if you find this solution helpful and you try to implement it, please tell me if you are successful in getting the public ip and port of the server-client connection on the server side. You can also answer my question about this on stackoverflow.
Please be specific, u may use GCDAsyncSocket to connect 2 phones, u may use sample code from Github.
Related
Conceptually I am unable to comprehend that how 2 devices, which are connected to their respective Wifi networks (for example) are able to establish a peer to peer connection, even with intermediate temporary server in between.
E.g. Computer A's public IP is 1.1.1.1 & private IP is 192.x.x.x. Computer B's public IP is 2.2.2.2 & private IP is 192.y.y.y. Without any firewall etc. (general case), how will they make a direct socket connection among them?
Will appreciate if you can explain in slightly layman's term.
Context: I am studying a server, which intends to provide WebRTC in the browser. Using Google's STUN server, they are able to exchange media in many cases. But conceptually I am unclear, on what takes place in between.
WebRTC uses a process called ICE for establishing the connection. Its a suite of techniques for NAT holepunching that mostly rely on the STUN protocol.
The formal description is in RFC 5245 (updated by a newer version)
This presentation from the IETF 92 is one of the best slide decks I've seen so far.
If I establish a connection with a friend on Skype, the audio and video data does not go through Microsoft but directly. I also have a p2p client X that does a similar thing. I do not fully understand how this happens internally. How does a machine establish the connection with the other if there is no direct identifier such as a public IP address? Multiple computers in the same network can each do p2p or Skype calls at the same time.
I have been wondering about this for a week because I want to connect two Nodes with each other (like a socket server/client). Can you point me in the right direction?
If two clients want to connect, but neither knows the address of the other, some sort of intermediary that they both know has to be in place to help set up the connection. They both contact the intermediary with the desire to connect, the intermediary tells them both what the others direct address is, and the connection can be set up directly.
Sometimes (read: always) one or both machines share a public IP with others behind NAT, and NAT traversal techniques are needed to establish end-to-end connectivity, usually some form of ICE or SIP.
I've read tons of questions about this all over the web, and can't seem to find a solid answer. If I have an iPhone that's running on cellular data and another iOS device on wifi (in two separate locations), is it possible for them to send data to each other directly without sending it first to a web server, then retrieving it? Are the only options sending and receiving from a server/Apple's iCloud? What if I knew the devices' ip addresses? Note that the iPhone has WiFi disabled.
I'm not looking to put this in the app store, it is for personal use. I know NSNotificationCenter isn't an option.
Using the gamekit framework you can send data between two iOS devices. It is easy to implement. Other than that I don't think there is any other way to send data between two iOS devices.
Actually, it IS possible. You may want to google for something called "UDP hole punching" or "TCP hole punching".
The main approach in short: Assuming you got something like a relay server, that is some server in the internet that is publicly addressable from every private LAN that is connected to the www. No you have your two clients A and B in (different) private LANs, with some Network address translation (NAT) going on, that want to establish a peer to peer connection.
First of all both will tell the server their IP address and the port they have in their own LAN. In the UDP or TCP packet, the server will find the public address and port of the device (or the NAT (router)). So the server knows the private and the public IP address as well as the ports.
If now A wants to communicate with B, it asks the server for help. The server will send a message to B that A wants to communicate with her telling her A's public and private IP and port. A gets back B's public and private information and port.
Now here is where the magic happens. Both clients now send packets out to establish a connection simultaneously to the private and public addresses of the other party and thus punching a whole in their NATs such that incoming connections will not be blocked. Even if one party's connection establishing packets will arrive before this whole is created, the other's packets will get through to such that a connection can be created.
Beware of some NATs that scan the data for IP addresses and translate them as well, but if you encrypt your data or change the appearance of the address (complement, ...) you will be fine.
Now the master question, how can the server communicate with one of the clients without an active connection. Well in this case you can use "connection reversal" and apple's "push notifications". Use the "push notifications" (pn) to tell a client behind a NAT that there is something of interest going on and that it should contact the server. Once it has done that the connection is active and can be used in the previous described fashion.
I hope this helps some people that get to this problem although the post is quite old!
You can only use direct IP address communications if the IP address are publicly reachable IP addresses accessible over the internet, and they are static (enough) so that they are not changing on you regularly as devices get assigned to addresses dynamically. In many (most) cases, that won't be true because your devices will be assigned their IP address dynamically and those addresses are frequently going to be self-assigned IP addresses that aren't publicly addressable.
As others have commented, using Apple-provided mechanisms like iCloud are probably the easiest options. If that's not something you'd like to entertain, there are probably ways to make use of a dynamic DNS service like DynDNS to manage the actual IP addresses of your devices. With something like that you might be able to use a direct IP connection between devices based on a named DNS lookup. You'd probably have to jump through some hoops to make that happen though and I'm not sure you'd want to go to that extent.
I think that Bluetooth would be a good option for you
I'm in the process of trying to write a chat application and I have a few issues
that I trying to work out. The application is basically a chat application that works on a Lan. One client acts as the
host and other clients can connect to the host and publicly chat among themselves. I want also the option of a client starting
a private chat with an already connected client. So what is the best way for this to happen. For example should the request message (which
contains the ip address of client) route through the host and then if the requested client wants to connect , then they initiate the connection
using ip of the requesting client. Should this also be on a separate port number. Does it matter if your application uses a number of ports.
Or, when ever a client connects to a host, the host should send them a list of users with there ip addresses, and then the client can
attempt a connection with the other client for a private chat.
Hope this all makes sense. Any help would be appreciated
Thanks
If you are just interested in a quick-and-dirty chat facility that only needs to work over a LAN, I'd suggest having all clients send and receive broadcast UDP packets on a single well-known port number. Then no server is necessary at all, and thus no discovery is necessary either, and things are a lot simpler.
If you really want to go the client-server route, though, you should have your server (aka host) machine accept TCP connections on a single well-known port, and then have it use select() or poll() to multiplex the incoming TCP connections and forward any data that comes in from each incoming TCP socket to all of the others sockets. Clients can connect via TCP to the server at this well-known port, but the clients will have to have some way of knowing what IP address to connect to... either from having the user type in the IP address of the server, or by some discovery mechanism (broadcast UDP packets could be used to implement that). This way is a lot more work though.
I'm all for creating my own but depending on time constraints sometimes I look for alternatives like this I used it in a company I worked at before. It's really good. But if you decide to make your own you first have to map out a logic, structure, Database and so on before you even think about code..
I've noticed that if you want to write an application that utilizes listening sockets, you need to create port forwarding rules on your router. If I want to connect two computers without either one of the the computers messing about with router settings, is there a way that I can get the two clients to connect to each other without either of them using listening sockets? There would need to be another server somewhere else telling them to connect but is it possible?
Some clarifications, and an answer:
Routers don't care about, or handle ports, that is the role of a firewall, which do port forwarding. The router/firewall combined device most of us have at home adds to the common misunderstanding.
Can you connect two computers without ServerSocket? No. You can use UDP (a stateless, connectionless communication protocol), but the role of a ServerSocket is to "listen" for incoming connection requests, and generate a Socket from those requests, which creates a communications channel between two endpoints. A Socket has both an InputStream and an OutputStream, so it can both read at write at either end. At that point (once the connection is made), the distinction between client/server is arbitrary, since a Socket is a two-way connection object, which allows both sides to send/receive.
What about proxying? Doesn't that allow connections between two computers without a ServerSocket? Well, no, because the server that's doing the proxying still has to be using a ServerSocket. Depending on what application you're trying to implement, this might be the way to go, or or might just add overhead. Even if there were "another server somewhere else telling them to connect", somebody has to listen for a connection request, which is the job of the ServerSocket.
If connections are happening over already open ports (most publicly accessible servers have ports <1024 not blocked by firewalls, but exceptions exist), then you shouldn't need to change firewall settings to get the connection to work.
So, to reiterate, the ONLY role of a ServerSocket (as far as your question is concerned) is to listen for incoming connection requests, and from those requests, create a Socket, which is a two-way communications channel between the two end points.
To answer the question, "How do I design a peer-to-peer app that avoids using listening sockets?", you don't. In the case of something like Vuze, the software acts as both client and server simultaneously, hence the term "peer", vs. "client" or "server" alone. In Vuze every client is a server, and every server (except for the tracker) is a client.
If you need a TCP connection between the 2 computers and both of them are behind routers (and you don't want to set up port forwarding) I think the only other possibility you have is having a third server somewhere that isn't behind a firewall running a ServerSocket and accepting connections between your 2 other computers and proxying communications between the 2. You can't establish a TCP Connection between the 2 without one listening to a socket and the other connecting to it.
Q: If I want to connect two computers without either one of the the
computers messing about with router settings, is there a way that I
can get the two clients to connect to each other
Yes: have the server listen on an open port :)